1. Field of the Invention
The present invention relates to a mobile communication method, a mobile communication system, and a radio base station by which uplink user data are transmitted at a transmission rate corresponding to a granted value notified to a mobile station by a cell under the control of a radio base station.
2. Description of the Related Art
In a mobile communication system employing an Enhanced Uplink (EUL) method defined by 3GPP, that is, High Speed Uplink Packet Access (HSUPA) method, a cell (a serving cell) under the control of a radio base station NodeB determines an initial value (initial granted value, Initial SG) of a SG (granted value, Scheduling Grant) to be notified to a mobile station UE in the following cases:
An uplink user data transmission channel (Enhanced-Dedicated Channel: E-DCH) is set up between the mobile station UE and the cell under the control of the radio base station NodeB (start of E-DCH transmission);
A serving cell for the mobile station UE is changed (E-DCH serving cell change); and
A change is made to a sub-frame (Transmission Time Interval: TTI) length in the uplink user data transmission channel (E-DCH) set up between the mobile station UE and the cell under the control of the radio base station NodeB (TTI change).
In addition, the mobile station UE is configured to transmit uplink user data via a set up uplink user data transmission channel at a transmission rate corresponding to an initial SG notified by a radio network controller RNC by use of an RRC message until receiving an SG notified by the serving cell under control of the radio base station NodeB (see 3GPP TS 25.321, 11.8.1.3.2 to 11.8.1.3.5).
However, in 3GPP, there is no definition on how the serving cell under the control of the radio base station NodeB determines the initial SG.
Accordingly, when the serving cell under the control of the radio base station NodeB sets an initial SG too large, received power of the uplink user data in the radio base station NodeB drastically changes. This causes a problem that the quality of receiving uplink user data in communication is deteriorated.